Air breathing, gas turbine engines conventionally employ a rotary compressor to provide compressed air that is ultimately used for two primary purposes. A first purpose is to serve as combustion air, that is, to provide the source of oxygen necessary to support oxidation of the fuel. A second purpose is to provide cooling of various engine components.
In a conventional radial turbine engine, for example, components requiring cooling by compressed air from the compressor include the combustor which typically is an annular combustor, the front turbine shroud, the rear turbine shroud and an annular nozzle and the vanes thereof. Usually, but not always, no separate provision is made for cooling the turbine wheel itself since much of the air used for cooling other components enters the stream of the gases of combustion to dilute the same such that the temperature of the gas impinging upon the turbine wheel is sufficiently low that the turbine wheel may readily be subjected to it without deleterious effects.
In the usual case, in order to cool the combustor, some means are typically provided in the form of openings in the combustor wall at various locations along with so-called cooling strips. As the combustor is typically disposed in a plenum connected to the outlet for the compressor, compressed air will enter the interior of the combustor through such apertures and be directed by the cooling strips along the interior of the combustor wall in a film-like flow regimen. The attachment of this flowing air film to the wall provides a buffer-like layer of air between the hot gases of combustion within the combustor and the combustor wall to prevent direct heat transfer between the same. Furthermore, a measure of convective cooling is provided as heat is transferred from the wall to the flowing air film.
This air ultimately serves as dilution air by mixing with the gases of combustion prior to the application of the same to the nozzle and ultimately to the turbine wheel. However, because it is mixed with the gases of combustion at this point in time, it cannot serve to provide a cooling function for the nozzle and/or the turbine wheel or, for that matter, turbine shrouds or the like. And because the output of any given compressor is limited, the use of air for cooling the interior surface of a combustor necessarily detracts from the amount of air available for directly cooling the turbine nozzle and/or shroud and/or turbine wheel.
This in turn limits the power density achievable within the combustor to a lower level than would be the case if more air could be utilized to cool the vanes and shrouds in order to assure that the same are not subjected to unduly high temperatures that would either shorten the life of the engine or require resort to exotic material of high cost for use in fabricating these components.
The present invention is directed to overcome one or more of the above problems.